| National City to Olympia Heights (Florida) | 2,256.76 mi (3,631.90 km) |
| National City to Omaha (Nebraska) | 1,300.14 mi (2,092.37 km) |
| National City to On Top of the World Designated Place (Florida) | 2,069.56 mi (3,330.63 km) |
| National City to Onalaska (Wisconsin) | 1,594.44 mi (2,566.01 km) |
| National City to Oneida (New York) | 2,345.05 mi (3,773.99 km) |
| National City to Oneonta (New York) | 2,372.89 mi (3,818.80 km) |
| National City to Ontario (California) | 99.35 mi (159.89 km) |
| National City to Ontario (Oregon) | 784.96 mi (1,263.27 km) |
| National City to Opa-locka (Florida) | 2,257.29 mi (3,632.76 km) |
| National City to Opelika (Alabama) | 1,838.12 mi (2,958.17 km) |
| National City to Opelousas (Louisiana) | 1,476.26 mi (2,375.81 km) |
| National City to Orange (California) | 89.08 mi (143.36 km) |
| National City to Orange (Texas) | 1,384.75 mi (2,228.54 km) |
| National City to Orange City (Florida) | 2,130.81 mi (3,429.21 km) |
| National City to Orangeburg (South Carolina) | 2,087.63 mi (3,359.72 km) |
